1. Field of the Invention
This invention relates to microwave ovens and in particular to means for sealing the stirrer shaft against leakage of RF energy outwardly through the opening through which the shaft extends to support the stirrer within the oven cavity.
2. Description of the Background Art
In one conventional form of microwave oven structure, a stirrer element is provided within the oven cavity for causing distribution of the microwave energy delivery to the cavity for uniform heating of the product being heated in the cavity by the microwave energy. The stirrer is conventionally mounted on the distal end of a stirrer shaft comprising the output drive shaft of an electric motor. The electric motor is conventionally mounted externally of the microwave oven cabinet and the stirrer shaft is passed through a hole in the cabinet to mount the stirrer within the cabinet.
One example of such structure is illustrated in U.S. Pat. No. 3,872,276 of Richard T. Corcoran et al. As shown therein, the stirrer motor shaft extends through a bushing mounted in the cabinet wall so as to permit the stirrer to be mounted for rotation within the oven cavity on the distal end of the stirrer shaft. Corcoran et al recognize that some means must be provided for sealing the shaft opening in the cabinet wall against energy leakage, but do not provide any specific means for effecting such sealing.
The later U.S. Pat. No. 4,053,730 of David Alan Baron et al, addresses the problem of sealing such an opening and more specifically teaches the provision of a metal plate, or disc, in closely spaced relationship to the cabinet wall while being maintained out of physical contact therewith. Baron et al teach the criticality of small spacing of the capacitive sealing disc from the cabinet wall and specify that the spacing should be about 0.125" or less for optimum benefits.
Arthur B. Poole, in U.S. Pat. No. 2,171,988, shows a synchronous electric motor structure wherein a cap portion of the housing is secured to the body portion thereof by a nut engaging a threaded portion of the shaft bushing and bearing against the cap to urge it in nested relationship to the main portion of the motor housing.
Michael J. Lettini et al disclose, in U.S. Pat. No. 3,922,050, an electrical terminal structure wherein a sleeve is caused to expand radially into low resistance electrical contact with a surrounding sheet or body member. The sleeve is extended through a cylindrical hole in the body member and the expansion thereof causes a radial outward engagement of the sleeve in the desired electrical contact with the sheet or body member.